Attribution of anthropogenic climate change contribution to heat-humidity stress in low-income homes, Khayelitsha, Cape Town

Thorburn, Jody

Attribution of anthropogenic climate change contribution to heat-humidity stress in low-income homes, Khayelitsha, Cape Town

Thesis / Dissertation

2026

Publisher

University of Cape Town

Department

Department of Environmental and Geographical Science

Faculty

Faculty of Science

Abstract

Anthropogenic climate change has significantly intensified extreme heat events across the world, posing severe health risks, particularly in low- and middle-income communities (LMICs). Research on humid-heat events and heat-humidity stress remains limited, especially within indoor environments in low-income settlements. Furthermore, no studies have assessed whether the frequency of indoor wet-bulb temperature (WBT) exceeding critical (20℃ – 32℃) and fatal (24℃ – 37℃) ranges (Lu & Romps, 2023) have changed over time, nor whether these changes can be attributed to anthropogenic climate change. This study investigated the extent to which anthropogenic climate change has influenced the frequency of indoor WBT exceeding these ranges in low-income homes in Khayelitsha Cape Town, South Africa. The investigation involved three main objectives: (1) conducting exploratory data analysis (EDA) to understand the relationship between indoor and outdoor environmental conditions, (2) developing predictive models to simulate past indoor WBT (1940 to 2024) for formal and informal homes, and (3) using a multi-method climate change probabilistic attribution approach, employing data from reanalysis and coupled climate models. The EDA revealed a strong correlation between indoor and outdoor conditions, with informal homes experiencing greater variability. Predictive modeling showed that outdoor temperature, relative humidity, and solar radiation significantly influenced indoor WBT. Reconstructed indoor WBT exceedances show a strong increasing trend since 1940 for both formal and informal homes. Attribution analysis further indicates that human-induced climate change has significantly increased the likelihood of experiencing critical and fatal exceedance events when compared to pre-industrial conditions (1860s). The reanalysis attribution revealed that reaching the lower fatal threshold of 24℃ was between 3 (95% CI: 0.78 - ∞) and 4 (95% CI: 0.11 – 8.90) times more likely in a world with climate change compared to one without, for formal and informal homes respectively. The coupled model-based attribution concluded the same, but with less significant probabilities (1.01 (95% CI: 1.00 – 1.02) and 1.03 (95% CI: 1.01 – 1.06) times more likely). Overall, informal homes were found to be more vulnerable to heat stress, likely due to structural characteristics, while formal homes experienced higher average WBTs, likely due to greater insulation. Furthermore, the urgent need for targeted climate adaptation strategies to protect already vulnerable communities, such as Khayelitsha, from the heat-related health risks associated with rising indoor heat-humidity stress is emphasised. Future research should focus on refining predictive models, accounting for behavioural adaptation, and exploring hybrid observational and climate model attribution analyses to improve robustness of conclusions made.

Keywords

climate change

heat-humidity stress

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